Unfortunately you do not mention what codec/filter you use.
Do you use ac3filter, which I very much prefer? (Can be downloaded here)
Or ... ?
Also you do not mention which version/build of BSPlayer you're using and whether you've got problems in full screen and/or in windowed mode.
E.g. in build 803 up-(arrow)key is the default key for Volume up in Windowed mode, but in Full screen mode the default "key" is mousewheel up.
You can change the defaults to you own liking through "Options"/"Preferences"/"Key definitions & WinLIRC". Note in build 803 you can set separate keys for Windowed mode and for Full screen mode (whereas in build 501 you cannot set separate keys for both modes).

__________________Help2Help (click)BSplayer: simply the best & most versatile (Build 1072 Dutch language here!)When posting always mention your computer's OS and the version and build number(!) of BS.Player as used by you,as well as - if applicable and especially when encountering problems - the type(s) of the file(s) mentioned in your post.Private messages/Visitor messages are NOT for seeking personal help with respect to BS.Player! Instead use the forums!